Ch.7.docx

Exteroceptive sensory systems – auditory, somatosensory, olfactory, gustatory
7.1 Principles of Sensory System Organization
primary cortex – most input from thalamic relay
secondary cortex­ most input from primary and other areas of the same system
Association – input from more than one system via secondary
Hierarchical Organization
Specific levels ­ receptors, thalamic relay nuclei, primary, secondary, association
Adds analysis
Higher level of damage, more specific the deficit
Sensation­ detecting presence of stimuli
Perception­ higher –order processing of integrating, recognizing and interpreting complete
patterns of sensation
Functional Segregation
Three areas contains functionally distinct areas that specialize in different analysis
Parallel Processing
Serial system – flow over one pathway – past
Parallal – simultaneous analysis of a signal in different ways by the multiple pathways
Two streams – one is conscious awareness and other is unconscious awareness
Summary Model of Sensory System Organization
Division of labor – multiple areas, levels and interconnected by pathways
Binding problem – stimuli are perceived as combined whole, rather than different ones Single area of cortex at top of hierarchy that receives from all systems and puts it together to form
perception
7.2 Auditory System
perception of sound – perception of objects through sound
vibrations of air molecules – 20 to 20, 000 hert
amplitude, frequency, and complexity = loudness, pitch, timbre
Pure tones – labs and recording studios only
Fourier analysis – mathematical procedure for breaking down complex waves into their component
sine waves
System F anal in terms of terms of sine waves
Pure­ relation between frequency and perceived pitch
Fundamental frequency – highest frequency of sound
Missing fundamental – all would be related to having a fundamental frequency of 100, because it’s
the pitch in pure tone
The Ear
Tympanic membrane ­ ear drum wavelengths cause it to vibrate
Ossicles – small bones of middle ear
Malleus – hammer
Incus­ anvil
Stapes­ stirrup
Vibrations of stapes trigger the oval window – transfers to cochlea( long coiled tube)
Organ of corti­ receptor
Basilar membrane­ hair cells
Tectorial membrane – rests on hair cells Deflection of organ causes force on hair then increases firing on axons of auditory nerve ­
branch of cranial nerve VIII
Vibrations of cochlear in round window – elastic membrane in cochlea wall
Humans – pure tones that are different by 0.2% ­ high freq stimulation close to window and low tip
of basilar membrane
Tonotopic mapping
Semicircular canals – receptive organs of the vestibular system – carries info about direction and
intensity of head movements which helps us maintain our balance
From the Ear to the Primary Auditory Cortex
no major pathway in system like visual – network of pathways
axons of each auditory nerve synapse – ipsilateral cochlear nuclei­ projections lead to superior
olives on both sides of brain stem at same level
axons of olivary neurons project via lateral lemnicsus to inferior colliculi­ synapse on neurons that
project to medial geniculate nuclei of thalamus – then primary auditory cotex
subcortical Mechanisms of Sound Localization
localization is mediated by lateral and medial superior olives
sound is louder in the ear it reaches first
some in medial sup olives respond to slight differences in time of arrival whereas some in lateral
respond to amplitude
project to sup and inf colluculus
map of auditory space
sup colliculi­ locating source of input in space
Auditory Cortex
Primates – tempora lobe has aud cortex, core region – surrounding is band called belt – secondary
Secondary outside of belt are parabelt
Organization of Primate Auditory Cortex
Functional columns – all vertical tend to respond to sounds in same frequency range Tonotopic mapping – frequency basis
What Sounds
Hierarchy
Two Streams of Cortex
Dorsal and ventral ­ prefrontal cortex and posterior cortex
Anterior is what and posterior is what
Auditory – Visual Interactions
Association cortex – not unimodal
Where does pitch perception occur
Anterior to primary cortex many neurons that responded to pitch – this area is where it changes
Effects of damage to Auditory System
Auditory Cortex Damage
Most is in lateral fissure
Bilateral lesions – complete loss of hearing – effects are loss of
localization and impairment of ability to discriminate freq
Unilateral – partially contralateral – ability to localize contralateral not
ipsilateral
Deafness in humans
most prevalent
severe damage is in inner ear or middle ear – rather than central
conductive deafness – ossicles
nerve deafness – cochlea or auditory nerve relations loss of hair cell receptors
if only part is damaged, then some frequencies so old people, high goes first
tinnitus – ringing of the ears – when one ear is damaged ringing seems to cme from that, cutting
nerve, no effect on ringing
cochlear implants­ bypass damage to hair cells by converting sounds picked by microphone to
electrical signals then carried to cochlea by bundle of electrodes – ecite auditory nerve
7.3 Somatosensory System: Touch and Pain
exeroceptive system –exteral
propricoceptive system – monitos info about position of body from muscles and balance
interoceptive – general things about conditions in the body
Deals with first which has mechanical – touch, thermal­ temp nociceptive­ pain
Cataneous Receptors
Free nerve endings – no specialized structure on them – sensitive to temp change and pain
Largest = pacinian corpuscles – adapt rapidly to sudden displacements of the ski, but not to
constant ressure
Merkels disks and Ruffini – adapt slow and respond to gradual skin indentation
Slow remain active after time and fast do not
Stereognosis­ identification of objects by touch
Slow and fast – dynamic and static qualities of tactual stimuli
Dermatomes
Carry info from cutaneous gather in nerves and enter spine via dorsal roots – innervated by left and
right dorsal roots
Overlap
Two Major Somatosensory Pathways
Dorsal column medial lemniscus – carry info about touch and proprioception Sensory neurons ente